If you require really high current/power gains, they can be obtained by using power MOSFET as the DC power switch.(I have seen this in a book some time ago). Most popular type is VFET family form Siliconix.VN66AF has a built in input protection zener diode. It can pass maximum currents of about 2A and has a typical saturation resistance of about 2 ohms.Hence if the device is used with a 12V supply, it will give a saturation voltage of about 80mV when used with a 300Ohm load or 1.091V when used with a 20ohm load.
Theoretically, DC power feed to loads such as lamps,heaters etc can easily be controlled via unidirectional sold state devices like bipolar transistors, power MOSFETs or SCRs which can be used in either the 'static' mode to give a simple on or off switch control action or in the pulsed mode to give a variable power control action. But each of these devices offer its own particular set of advantages/disadvantages.(These are my notes from high school)